Make sure that not maximized clients are offscreen on xrandr events

Added a small check in Client::checkWorkspacePosition which will assure
us that no window ("client") is left in a offscreen position. this is
more a workaround than a proper fix but is the only thing we can do that
will be backportable to the 4.7 branch.

geometry.cpp

@@ -1154,6 +1154,15 @@ void Client::checkWorkspacePosition(const QRect &geo)
                                   newGeom.x() + newGeom.width() - 1));
         }
 
+        if (newGeom.x() > screenArea.right()) {
+            int screenWidth = screenArea.width();
+            newGeom.moveLeft(screenWidth - (screenWidth / 4));
+        }
+        if (newGeom.y() > screenArea.bottom()) {
+            int screenHeight = screenArea.height();
+            newGeom.moveBottom(screenHeight - (screenHeight / 4));
+        }
+
         // Obey size hints. TODO: We really should make sure it stays in the right place
         newGeom.setSize(adjustedSize(newGeom.size()));